The present invention generally relates to signal modulation, such as for radiofrequency signal generation, and particularly relates to modulation waveforms and corresponding modulation circuits.
Transmitters used in communication devices and systems commonly employ modulation circuits to up-convert baseband information signals to a desired (carrier) frequency. More particularly, such devices and systems impose transmit information on carrier signals, which usually are generated at desired or assigned transmit channel frequencies, by modulating carrier signal phase, frequency, amplitude, or some combination thereof, according to one or more baseband information signals representing the desired transmit information.
Quadrature modulation, also referred to as “IQ” modulation, uses two carrier signals, an in-phase carrier and quadrature carrier that is offset from the in-phase carrier by 90 degrees. The two carriers generally are modulated by corresponding in-phase and quadrature baseband information signals and then combined for amplification and transmission over a communication channel. IQ modulation finds widespread use in a variety of wireless communication systems, such as in cellular communication networks based on Wideband Code Division Multiple Access (WCDMA) or cdma2000 standards.